Process for producing expandable polylactic acid-containing pellets

The invention relates to a process for producing expandable polylactic acid-containing pellets, comprising the steps of: a) melting and mixing in the following components: i) 65% to 95% by weight, based on the total weight of components i to iii, of polylactic acid, where the polylactic acid is composed of proportions of: ia) 65% to 95% by weight of polylactic acid having a D-lactic acid content of 0.3% to 5% by weight and ib) 5% to 3% by weight of polylactic acid having a D-lactic acid content of 10% to 18% by weight; ii) 15% to 35% by weight, based on the total weight of components i to iii, of an aliphatic polyester selected from the group consisting of polybutylene succinate, polybutylene succinate-co-adipate and polybutylene succinate-co-sebacate; iii) 0% to 2% by weight, based on the total weight of components i to iii, of a compatibilizer; iv) 0.1% to 5% by weight, based on the total weight of components i to iii, of an additive, b) mixing v) 1% to 7% by weight, based on the total weight of components i to iv, of an organic blowing agent and vi) 0.01% to 5% by weight of a co-blowing agent - selected from the group of nitrogen, carbon dioxide, argon, helium and mixtures thereof - into the polymer melt by means of a static or dynamic mixer at a temperature of at least 140°C, c) discharging through a die plate having bores having a diameter at the die exit of not more than 1.5 mm and d) pelletizing the blowing agent-containing melt directly beyond the die plate underwater at a pressure in the range from 1 to 21 bar.